Field of the Invention
The present invention relates to a catalyst for purification of exhaust gas. More specifically, the present invention relates to: a catalyst for purification of exhaust gas, comprising a noble metal and a catalyst support comprising ceria supported on a surface of a composite oxide composed of alumina, zirconia, and titania; a NOx storage-reduction catalyst comprising the catalyst for purification of exhaust gas and a NOx storage material; and a method for purifying exhaust gas by using the NOx storage-reduction catalyst.
Related Background Art
To purify harmful hydrocarbons (HC) and carbon monoxide (CO) contained in exhaust gas from an internal combustion engine, catalysts for purification of exhaust gas have been utilized in the combustion reaction. Moreover, to purify harmful nitrogen oxides (NOx) contained in oxygen-excessive exhaust gas, NOx storage-reduction catalysts capable of subjecting NOx to storage reaction and/or reduction reaction have been utilized. However, exhaust gas contains SO2 generated by burning sulfur contained in a fuel, and this SO2 brings about a problem that such a catalyst for purification of exhaust gas and a NOx storage material are poisoned and deteriorate. For this reason, a catalyst support containing titania has been used in the catalysts for purification of exhaust gas and NOx storage-reduction catalysts which are required to have a sulfur-poisoning resistance.
For example, Japanese Unexamined Patent Application Publication No. 2004-321847 (Patent Literature 1) discloses, as a NOx storage-reduction catalyst having a sulfur-poisoning resistance, a catalyst comprising: a catalyst support comprising a composite oxide composed of alumina, zirconia, and titania, at least a part of the titania being dissolved in the alumina in the form of solid solution; and a noble metal and a NOx storage material which are supported on the catalyst support.
Moreover, Japanese Unexamined Patent Application Publication No. 2008-137886 (Patent Literature 2) discloses a catalyst for purification of exhaust gas (NOx storage-reduction catalyst), comprising Pt, Ce, and Ba supported on a support comprising alumina, a zirconia-titania composite oxide, Rh-supporting zirconia, and a ceria-zirconia composite oxide.